It is common in the field of transport refrigeration to selectively operate a refrigerant compressor via one of two prime movers. A first prime mover includes an internal combustion engine, such as a diesel engine, and a centrifugal or electric clutch; and, a second prime mover includes an electric drive motor. The engine and clutch drive the compressor while the associated truck, trailer, container, and the like, is away from a terminal, and the electric motor drives the compressor while the refrigeration system is accessible to a source of electrical potential, such as at a terminal or on board a ship. U.S. Pat. Nos. 3,720,842; 3,941,012; 4,616,743; 4,811,569; 4,846,327; and 5,105,096, all of which are assigned to the same assignee as the present application, illustrate arrangements for selectively and alternatively utilizing an internal combustion engine or an electric motor to drive a refrigerant compressor.
It would be desirable, and it is a first object of the invention, to be able to interlock the selection and operation of the engine and drive motor, to prevent energization of the electric motor while the engine is operative, and to de-energize the electric motor when running if starting of the engine is attempted.
It would also be desirable, and it is another object of the invention, to be able to detect slippage of the clutch disposed between the internal combustion engine and the refrigerant compressor.
It would also be desirable, and it is still another object of the invention, to be able to detect improper rotational direction of an evaporator fan motor, to provide back-up protection in the event an electrical phase detector is faulty, improperly connected, or not used.